IEC 61672-2:2013

IEC 61672-2 ®
Edition 2.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electroacoustics – Sound level meters –
Part 2: Pattern evaluation tests

Electroacoustique – Sonomètres –
Partie 2: Essais d'évaluation d'un modèle

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IEC 61672-2 ®
Edition 2.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electroacoustics – Sound level meters –

Part 2: Pattern evaluation tests

Electroacoustique – Sonomètres –

Partie 2: Essais d'évaluation d'un modèle

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX W
ICS 17.140.50 ISBN 978-2-8322-1080-2

– 2 – 61672-2 © IEC:2013
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Submission for testing . 7
5 Marking of the sound level meter and information in the Instruction Manual . 8
6 Mandatory facilities and general requirements . 8
7 Environmental, electrostatic, and radio-frequency tests . 10
7.1 General . 10
7.2 Uncertainties for measurements of environmental test conditions . 11
7.3 Influence of static pressure . 11
7.4 Limits on air temperature, relative humidity and static pressure . 12
7.5 Acclimatization requirements for tests of the influence of air temperature and
relative humidity . 12
7.6 Abbreviated test of the combined influence of air temperature and relative
humidity . 12
7.7 Influence of air temperature . 14
7.8 Influence of relative humidity . 15
7.9 Influence of electrostatic discharges . 16
7.10 Influence of a.c. power-frequency and radio-frequency fields. 17
7.10.1 Sound signal . 17
7.10.2 AC power-frequency tests . 17
7.10.3 Radio-frequency tests . 17
8 Radio-frequency emissions and public power supply disturbances. 19
9 Electroacoustical performance tests . 20
9.1 General . 20
9.2 Indication at the calibration check frequency . 21
9.3 Directional response . 21
9.4 Tests of frequency weightings with acoustical signals . 23
9.4.1 General . 23
9.4.2 Windscreen corrections . 24
9.4.3 Free-field tests . 24
9.4.4 Comparison coupler tests . 25
9.4.5 Conformance . 26
9.4.6 Random incidence . 26
9.5 Tests of frequency weightings with electrical signals . 27
9.5.1 General . 27
9.5.2 First alternative test procedure (variable input signal level). 27
9.5.3 Second alternative test procedure (constant input signal level) . 27
9.5.4 Conformance . 28
9.5.5 Frequency weightings C or Z at 1 kHz . 28
9.6 Corrections for the effect of reflections from the case of a sound level meter
and diffraction around a microphone . 28
9.7 Corrections to obtain free-field or random-incidence sound levels . 29
9.8 Level linearity . 30
9.8.1 Tests at an air temperature near the reference air temperature . 30
9.8.2 Tests at elevated air temperature . 31

61672-2 © IEC:2013 – 3 –
9.9 Under-range indication . 31
9.10 Self-generated noise level . 31
9.11 Decay time constants for time weightings F and S . 32
9.12 Toneburst response for sound level meters that measure time-weighted
sound level . 32
9.13 Toneburst response for sound level meters that measure sound exposure
level or time-averaged sound level . 33
9.14 Response to sequences of repeated tonebursts for sound level meters that
measure time-averaged sound level . 34
9.15 Overload indication . 34
9.16 C-weighted peak sound level . 35
9.17 Reset . 36
9.18 Electrical output . 36
9.19 Timing facilities . 36
9.20 Crosstalk in multi-channel sound level meter systems . 36
9.21 Power supply . 36
10 Pattern evaluation report . 37
Bibliography . 38

– 4 – 61672-2 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROACOUSTICS –
SOUND LEVEL METERS –
Part 2: Pattern evaluation tests

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61672-2 has been prepared by IEC technical committee 29,
Electroacoustics, in cooperation with the International Organization of Legal Metrology
(OIML).
This second edition cancels and replaces the first edition published in 2003. This second
edition constitutes a technical revision.
The main technical changes with regard to the previous edition are as follows:
In this second edition, conformance to specifications is demonstrated when:
a) measured deviations from design goals do not exceed the applicable acceptance limits,
and
b) the uncertainty of measurement does not exceed the corresponding maximum permitted
uncertainty, with both uncertainties determined for a coverage probability of 95 %.

61672-2 © IEC:2013 – 5 –
The text of this second edition is based on that of the first edition and the following
documents:
FDIS Report on voting
29/813/FDIS 29/824/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61672 series, published under the general title Electroacoustics –
Sound level meters, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – 61672-2 © IEC:2013
ELECTROACOUSTICS –
SOUND LEVEL METERS –
Part 2: Pattern-evaluation tests

1 Scope
This part of IEC 61672 provides details of the tests necessary to verify conformance to all
mandatory specifications given in IEC 61672-1 for time-weighting sound level meters,
integrating-averaging sound level meters, and integrating sound level meters. Pattern-
evaluation tests apply for each channel of a multi-channel sound level meter, as necessary.
Tests and test methods are applicable to class 1 and class 2 sound level meters. The aim is
to ensure that all laboratories use consistent methods to perform pattern-evaluation tests.
NOTE 1 In this document, references to IEC 61672-1, IEC 61672-2, and IEC 61672-3 refer to the second editions
unless stated otherwise.
NOTE 2 Procedures for the pattern-evaluation testing of sound level meters designed to conform to the
specifications of IEC 61672-1:2002 were given in IEC 61672-2:2003.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60942, Electroacoustics – Sound calibrators
IEC 61000-4-2:2008, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test
IEC 61000-4-3:2010, Electromagnetic compatibility (EMC) – Part 4-3: Testing and
measurement techniques – Radiated, radio-frequency, electromagnetic-field immunity test
IEC 61000-4-6:2008, Electromagnetic compatibility (EMC) – Part 4-6: Testing and
measurement techniques – Immunity to conducted disturbances, induced by radio-frequency
fields
IEC 61000-6-2:2005, Electromagnetic compatibility (EMC) – Part 6-2: Generic standards –
Immunity for industrial environments
IEC 61094-1, Measurement microphones – Part 1: Specifications for laboratory standard
microphones
IEC 61094-5, Measurement microphones – Part 5: Methods for pressure calibration of working
standard microphones by comparison
IEC 61183, Electroacoustics – Random-incidence and diffuse-field calibration of sound level
meters
IEC 61672-1, Electroacoustics – Sound level meters – Part 1: Specifications

61672-2 © IEC:2013 – 7 –
IEC 62585, Electroacoustics – Methods to determine corrections to obtain the free-field
response of a sound level meter
CISPR 16-1-1, Specification for radio disturbance and immunity measuring apparatus and
methods – Part 1-1: Radio disturbance and immunity measuring apparatus – Measuring
apparatus
CISPR 16-1-2:2006, Specification for radio disturbance and immunity measuring apparatus
and methods – Part 1-2: Radio disturbance and immunity measuring apparatus – Ancillary
equipment – Conducted disturbances
CISPR 16-2-1:2010 (Ed. 2.1), Specification for radio disturbance and immunity measuring
apparatus and methods – Part 2-1: Methods of measurement of disturbances and immunity –
Conducted disturbance measurements
CISPR 16-2-3:2010 (Ed. 3.1), Specification for radio disturbance and immunity measuring
apparatus and methods – Part 2-3: Methods of measurement of disturbances and immunity –
Radiated disturbance measurements
CISPR 22:2008, Information technology equipment – Radio disturbance characteristics –
Limits and methods of measurement
ISO/IEC Guide 98-3, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM: 1995)
ISO/IEC Guide 99, International vocabulary of metrology – Basic and general concepts and
associated terms (VIM)
ISO 26101:2012, Acoustics – Test methods for the qualification of free-field environments
3 Terms and definitions
For the purposes of this document, in addition to the terms and definitions given in
IEC 61672-1 and IEC 62585, the terms and definitions given in IEC 61000-4-2,
IEC 61000-4-3, IEC 61000-4-6, ISO/IEC Guide 98-3, and ISO/IEC Guide 99 also apply.
4 Submission for testing
4.1 At least three specimens of the same pattern of sound level meter shall be submitted
for pattern-evaluation testing. As a minimum, the laboratory shall select two of the specimens
for testing. At least one of the two specimens shall then be tested fully according to the
procedures of this Standard. The laboratory shall decide whether the full tests shall also be
performed on the second specimen or whether additional limited testing is adequate to
approve the pattern.
4.2 An Instruction Manual and all items or accessories that are identified in the Instruction
Manual as integral components for the normal mode of operation shall be submitted along
with the three sound level meters. Examples of additional items or accessories include a
microphone extension device or cable and peripheral equipment.
4.3 If the manufacturer of the sound level meter supplies devices that are to be connected
to the sound level meter by cables, then the devices and cables shall be submitted with the
sound level meter.
—————————
In English, CISPR stands for International Special Committee on Radio Interference.

– 8 – 61672-2 © IEC:2013
4.4 A calibrated sound calibrator of a model specified in the Instruction Manual for the
sound level meter shall be supplied with the sound level meter. An Instruction Manual for the
sound calibrator shall also be provided. As required by IEC 61672-1, the model of the
calibrator shall conform to the relevant specifications of IEC 60942 for the class of sound
calibrator.
5 Marking of the sound level meter and information in the Instruction Manual
5.1 It shall be verified that the sound level meter is marked according to the requirements
of IEC 61672-1.
5.2 It shall be verified that the Instruction Manual contains all the information that is
required by IEC 61672-1, as relevant to the facilities provided by the sound level meter.
5.3 If the sound level meter does not conform to the requirements of 5.1 and 5.2, no
pattern-evaluation tests shall be performed.
5.4 After completion of all tests, the information shall be reviewed to ensure that it is
correct and that no applicable acceptance limits are exceeded.
6 Mandatory facilities and general requirements
6.1 No test specified in this part of IEC 61672 shall be omitted unless the sound level
meter does not possess the facility described for the test. When the design of a sound level
meter, which has been pattern approved, is changed and a new pattern approval is requested,
then, at the discretion of the laboratory, it is not necessary to repeat those tests for
electroacoustical performance characteristics that are not affected by the design change.
6.2 A time-weighting sound level meter shall be verified to be able to display A-frequency-
weighted, F-time-weighted sound level and to be able to indicate overload and under-range
conditions.
6.3 An integrating-averaging sound level meter shall be verified to be able to display A-
frequency-weighted, time-averaged sound level and to be able to indicate overload and
under-range conditions.
6.4 An integrating sound level meter shall be verified to be able to display A-frequency-
weighted sound exposure level and to be able to indicate overload and under-range
conditions.
6.5 All display devices for the sound level meter shall be verified to be able to display
sound levels or sound exposure levels with the resolution required by IEC 61672-1. The range
of the display shall be at least the minimum specified in IEC 61672-1.
6.6 If a sound level meter is capable of measuring maximum or peak sound levels, or both,
it shall be verified that a "hold" feature is provided.
6.7 A class 1 sound level meter shall be verified to have frequency-weighting C.
6.8 If the sound level meter is capable of indicating C-weighted peak sound levels, it shall
be verified that the capability to display C-weighted, time-weighted sound level or C-weighted,
time-averaged sound level is also provided.
6.9 For sound level meters with multiple level ranges, it shall be verified that overlap of the
level ranges conforms to the specifications of IEC 61672-1.

61672-2 © IEC:2013 – 9 –
6.10 For sound level meters that can display more than one measurement quantity, it shall
be verified that there is a means to ascertain the quantity that is being displayed.
6.11 If the sound level meter does not possess the mandatory facilities listed in 6.2 through
6.10, as applicable, the sound level meter does not conform to the specifications of
IEC 61672-1 and no pattern-evaluation tests shall be performed.
6.12 For all pattern-evaluation tests, the configuration of the sound level meter, or the multi-
channel sound level meter system, shall be as specified in the Instruction Manual for one of
the normal modes of operation, including all required accessories. The configuration shall
include a windscreen if a windscreen is an integral component for the normal mode of
operation, or if the Instruction Manual states that the sound level meter conforms to the
specifications of IEC 61672-1 with a windscreen installed around the microphone. The model
of the windscreen shall be as stated in the Instruction Manual for use with the sound level
meter. All configurations of the sound level meter that are stated in the Instruction Manual as
conforming to the requirements of IEC 61672-1 shall be tested.
6.13 If the Instruction Manual states that the sound level meter conforms to the
specifications of IEC 61672-1 with optional facilities installed, the configuration with the
optional facilities installed shall also be tested to verify conformance to the relevant
specifications.
6.14 If an electrical output is provided on the sound level meter and the laboratory intends to
utilize the electrical output instead of the display device, the laboratory shall verify that
changes in the levels of applied acoustical or electrical input signals produce changes in the
signal levels indicated on the display device and at the electrical output that are in
accordance with the specifications of IEC 61672-1. This requirement applies to each channel
of a multi-channel system. Where multiple outputs are present, if an output is specified in the
Instruction Manual for testing, that output should be used for pattern-evaluation tests.
For all tests, the sound level meter shall be powered from its preferred supply.
6.15
6.16 The sound level meter shall be allowed to reach equilibrium with the prevailing
environmental conditions before switching on the power to perform a test.
6.17 Tests for conformance to the specifications for the effects of changes in environmental
conditions preferably should be conducted before tests for conformance to the specifications
for electroacoustical performance.
6.18 If the sound level meter has more than one signal-processing channel, pattern-
evaluation tests shall be performed for each channel that utilizes unique signal processing
techniques. For multi-channel systems with the same functional equivalence in all channels,
the number of channels to be tested may be less than the number of available channels, at
the discretion of the laboratory. For a multi-channel system, the number of channels to be
tested should be determined from consideration of a scenario for which there is an array of
microphones supplying signals to each input with each channel processing the signals in an
identical manner. Selection of how many and which channels to test should consider
differences, as described in the Instruction Manual, in the implementation of signal-processing
techniques in the various channels. If any special procedure for testing the channels for
identical functionality is described in the Instruction Manual, that procedure should be
followed.
NOTE If the sound level meter is a multi-channel device (for example, a sound level meter with two or more
separate signal inputs with non-parallel processing of digitized data by time-sharing, but quasi-parallel display for
the displayed signals), it is usually possible to test the channels for identical functionality either by setting the
functions of the channels for identical processing and reading the display(s) or by allowing the channel functionality
to rotate by a special test setting procedure thereby allowing comparison of display(s).
6.19 Conformance to a performance specification is demonstrated when the following criteria
are both satisfied: (a) a measured deviation from a design goal does not exceed the

– 10 – 61672-2 © IEC:2013
applicable acceptance limit and (b) the corresponding uncertainty of measurement does not
exceed the corresponding maximum-permitted uncertainty of measurement given in
IEC 61672-1 for the same coverage probability of 95%. IEC 61672-1 gives example
assessments of conformance using these criteria.
6.20 The laboratory shall use instruments with current calibrations for the appropriate
quantities. The calibrations shall be traceable to national standards, as required.
6.21 Laboratories performing pattern evaluation tests shall calculate all uncertainties of
measurements in accordance with the guidelines given in the ISO/IEC Guide 98-3. Actual
measurement uncertainties shall be calculated for a coverage probability of 95 %. Calculation
of the actual measurement uncertainty for a particular test should consider at least the following
components, as applicable.
– The uncertainty attributed to calibration of the individual instruments and equipment used
to perform the test, including the sound calibrator, where applicable;
– The uncertainty resulting from environmental effects or corrections;
– The uncertainty resulting from small errors that may be present in the applied signals;
– The uncertainty attributed to effects associated with the repeatability of the results of the
measurements. When a laboratory is only required to perform a single measurement, it is
necessary for the laboratory to make an estimate of the random contribution to the total
measurement uncertainty. The estimate should be determined from an earlier evaluation
of several measurements of the performance of similar sound level meters;
– The uncertainty associated with the resolution of the display device of the sound level
meter under test. For digital display devices that indicate signal levels with a resolution of
0,1 dB, the uncertainty component should be taken as a rectangular distribution with semi-
range of 0,05 dB;
– The uncertainty associated with the device used to mount the sound level meter in the
free-field test facility;
– The uncertainty resulting from the deviation of the sound field in the free-field test facility
from an ideal free sound field; and
– The uncertainty associated with each correction applied to the measurement data.
6.22 If the uncertainty of measurement exceeds the maximum-permitted uncertainty of
measurement, the result of the test shall not be used to demonstrate conformance to a
specification and pattern approval shall not be granted.
6.23 As appropriate, the laboratory shall utilize the recommendations given in the Instruction
Manual for performing the pattern-evaluation tests.
7 Environmental, electrostatic, and radio-frequency tests
7.1 General
7.1.1 Before conducting, but not during, the tests described in the Clause 7, the indication
of A-weighted sound level at the calibration check frequency shall be checked by application
of the sound calibrator specified in 4.4. If necessary, the sound level meter shall be adjusted
to indicate the required sound level under reference environmental conditions. For multi-
channel devices, the corresponding indications shall be checked for all channels selected for
testing.
7.1.2 Environmental conditions at the time of checking the indication shall be recorded.
7.1.3 The effect of environmental conditions on the sound pressure level produced by the
sound calibrator shall be accounted for in accordance with the procedure in the Instruction

61672-2 © IEC:2013 – 11 –
Manual for the sound calibrator and data from its calibration. The effects shall be evaluated
relative to the sound pressure level produced under reference conditions.
7.1.4 For environmental tests, a sound calibrator shall be used to provide a known sound
pressure level at the microphone of the sound level meter. For class 1 sound level meters, the
calibrator shall conform to either the class LS or class 1 specifications of IEC 60942. For
class 2 sound level meters, the calibrator shall conform to either class LS, class 1, or class 2
specifications of IEC 60942. If the sound calibrator conforms to the requirements of the
applicable performance class for a nominal frequency of 1 kHz, the environmental tests shall
be performed at the nominal frequency of 1 kHz. The effects of static pressure, air
temperature, and relative humidity on the sound pressure level produced in the coupler of the
sound calibrator, over the range of environmental conditions specified for the tests, shall be
known.
NOTE The range of environmental conditions specified for pattern-evaluation tests exceeds the range specified in
IEC 60942 for class LS sound calibrators.
7.1.5 The sound level meter shall be set to perform a typical measurement of time-weighted
sound level, time-averaged sound level, or sound exposure level on the reference level range.
The frequency weighting shall be set to A weighting.
7.1.6 Time-weighted sound levels, time-averaged sound levels, or sound exposure levels
indicated by the sound level meter in response to the signal from the sound calibrator shall be
recorded for each test condition. When necessary, time-averaged sound levels shall be
calculated from the indications of sound exposure level and elapsed time in accordance with
IEC 61672-1. Averaging times for time-averaged sound levels or integration times for sound
exposure levels shall be recorded.
7.2 Uncertainties for measurements of environmental test conditions
The actual uncertainty of measurement shall not exceed 0,2 kPa for measurements of static
pressure. The actual uncertainty of measurement shall not exceed 0,3 °C and 4 % relative
humidity for measurements of air temperature and relative humidity, respectively. These
measurement uncertainties shall be determined for a coverage probability of 95 %,
7.3 Influence of static pressure
7.3.1 During the measurements of the influence of static pressure, the measured air
temperature shall be within ±2,0 °C of the reference air temperature. Measured relative
humidity at the reference static pressure shall be maintained within +20 % relative humidity to
–10 % relative humidity from the reference relative humidity.
7.3.2 For practical reasons, relative humidity is specified for the reference static pressure.
Evacuating or pressurizing an enclosure around a sound level meter will change the relative
humidity within the enclosure. No corrections for this effect shall be applied.
7.3.3 The influence of static pressure shall be tested at the reference static pressure and
at seven other static pressures. At each static pressure, the sound calibrator of 7.1.4 and the
sound level meter (or its relevant components) shall be permitted to acclimatize for at least
10 minutes before recording the indicated sound level. For tests of the influence of static
pressure, the sound calibrator shall remain coupled to the microphone of the sound level
meter during the acclimatization periods. The electrical power applied to the sound level
meter may be on continuously, or may be switched off and on by remote means.
7.3.4 Sound levels shall be measured twice at nominal static pressures spaced at
approximately equal intervals between the minimum and the maximum static pressure
specified in IEC 61672-1. For each nominal static pressure condition, the two measured static
pressures shall not differ by more than 1 kPa. One measurement sequence shall start from
the minimum static pressure and increase to each selected nominal pressure until the
maximum is reached. The other sequence shall follow a decrease in pressure from the

– 12 – 61672-2 © IEC:2013
maximum via each of the selected nominal pressures until the minimum is reached. At the
maximum static pressure, only one indication of sound level shall be recorded.
7.3.5 The indicated sound levels shall be corrected for any difference between the sound
pressure level generated by the sound calibrator under a test condition and the sound
pressure level generated under reference environmental conditions.
7.3.6 At each static pressure test condition, the measured deviation of the indicated sound
level from the sound level first indicated at the reference static pressure shall not exceed the
applicable acceptance limits specified in IEC 61672-1.
7.4 Limits on air temperature, relative humidity and static pressure
Unless specified otherwise, for each test of the influence of air temperature and relative
humidity, including the acclimatization requirements given in 7.5, the measured air
temperature shall not exceed ±1,0 °C of a specified air temperature, the measured relative
humidity shall not exceed ±5 % relative humidity of a specified relative humidity, and the
measured difference between the maximum and minimum prevailing static pressures shall not
exceed 6,0 kPa.
7.5 Acclimatization requirements for tests of the influence of air temperature and
relative humidity
7.5.1 The sound calibrator of 7.1.4 and the sound level meter (or relevant components)
shall be placed in an environmental chamber to test the influence of air temperature and
relative humidity on the sound level meter.
7.5.2 For tests of the influence of air temperature and relative humidity, the sound
calibrator and the microphone on the sound level meter shall be uncoupled and the power to
both instruments switched off during an acclimatization period.
7.5.3 The sound calibrator and sound level meter shall be permitted to acclimatize at the
reference environmental conditions for at least 12 h.
7.5.4 For all test conditions other than reference environmental conditions, the sound
calibrator and sound level meter shall be permitted to acclimatize for at least an additional 7 h
after completion of the initial 12 h acclimatization period, unless the laboratory has applicable
evidence that a shorter acclimatization period is sufficient.
7.5.5 After completion of an acclimatization period, the sound calibrator shall be coupled to
the microphone of the sound level meter and the power switched on to both instruments.
7.5.6 The laboratory may have the facility to couple the sound calibrator to the microphone
of the sound level meter without affecting the temperature and relative humidity in the
environmental test chamber. If this facility is available, sound levels may be recorded
following the time specified in the Instruction Manual for pressure equalization of the
microphone. If this facility is not available, at least a further 3 h acclimatization time shall be
allowed before commencing a test.
7.6 Abbreviated test of the combined influence of air temperature and relative
humidity
7.6.1 To reduce the time and cost of verifying the influence of air temperature and relative
humidity on the performance of a sound level meter, a set of abbreviated tests shall first be
performed for certain combinations of air temperature and relative humidity.
7.6.2 For the abbreviated tests of the combined influence of air temperature and relative
humidity, the acceptance limits are smaller than those specified in IEC 61672-1. If the sound

61672-2 © IEC:2013 – 13 –
level meter conforms to the reduced acceptance limits at all specified test conditions, then the
sound level meter shall be considered to fully conform to the temperature and humidity
specifications of IEC 61672-1. No additional tests are required. If the sound level meter fails
to conform to the reduced acceptance limits for any specified test condition, then additional
temperature and humidity tests shall be performed to determine conformance to the
specifications of IEC 61672-1. The additional tests are described in 7.7 and 7.8.
7.6.3 Following the acclimatization procedures described in 7.5, the sound level indicated
in response to application of the sound calibrator of 7.1.4 shall be recorded for certain
combinations of air temperature and relative humidity. When setting the test conditions, rapid
changes of air temperature in the test chamber should be avoided. Care should be taken to
avoid condensation while the temperature is being changed in the environmental test
chamber. It is important to monitor the relative humidity in the environmental test chamber
each time the air temperature is changed to ensure that the relative humidity does not exceed
the specified range.
NOTE The combinations of temperature and relative humidity in 7.6.4 and 7.6.5 were chosen in consideration of
the dewpoints that were obtainable within available environmental test facilities. The combinations also reflect the
range of environmental conditions for general applications of class 1 and class 2 sound level meters.
7.6.4 For sound level meters where all components can be operated over the wide range
of temperature and relative humidity covered by the specifications in IEC 61672-1, the target
test conditions are given below. The reference air temperature and the reference relative
humidity are given in IEC 61672-1.
• for class 1 sound level meters:
– reference air temperature and reference relative humidity,
– air temperature of -10 °C and relative humidity of 65 %,
– air temperature of +5 °C and relative humidity of 25 %,
– air temperature of +40 °C and relative humidity of 90 %, and
– air temperature of +50 °C and relative humidity of 50 %.
• for class 2 sound level meters:
– reference air temperature and reference relative humidity,
– air temperature of 0 °C and relative humidity of 30 %, and
– air temperature of +40
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